So, what gives? Is it possible to have a 60/67 match in a different subclade? Or did either Ethnoancestry or FTDNA make a mistake? Using the rule of thumb of about 150 years per unit of genetic distance at 67 markers, Rick and Bryan shared a y-dna ancestor about 1,050 years ago. Even if we doubled that estimated TMRCA, that would only get us back 2100 years. And I don't think anyone believes L21 is quite that young.

My conclusion is that Rick and Bryan are either BOTH L21+ or BOTH L21-.

I've been puzzled about this. What process might cause this "lack of divergence" for some haplotypes in different subclades?

A subject I've often wondered about myself, I have a GD of 0 at 37 with a person sharing my name were there should be no chance of a connection within the last 250 yrs at least, they’re in the US were as I’m in the UK, conversely we have another two people with a paper trail going back to about 1725 with a GD of 4 at 37, I might add that the name is not that common, there are only 17 people with it in FTDNA's database.

I've been puzzled about this. What process might cause this "lack of divergence" for some haplotypes in different subclades?

Nothing really causes it, per se. It just so happens that some lines of descent have had (by chance) fewer mutations than other lines or even than the average line.

If you give 100 men a coin, and have each one flip it one hundred times then most of them will end up with something close to 50 heads and 50 tails. But, by chance, some of them will end up with significantly less than 50 heads.

Likewise, in a large group of men most of them will have haplotypes that have diverged from their 100-generation-ago ancestor by a decent amount (a GD of 10 to 15, for example). But some will diverge much less, while others will diverge much more. It's really just luck.

I've been puzzled about this. What process might cause this "lack of divergence" for some haplotypes in different subclades?

Nothing really causes it, per se. It just so happens that some lines of descent have had (by chance) fewer mutations than other lines or even than the average line.

If you give 100 men a coin, and have each one flip it one hundred times then most of them will end up with something close to 50 heads and 50 tails. But, by chance, some of them will end up with significantly less than 50 heads.

Likewise, in a large group of men most of them will have haplotypes that have diverged from their 100-generation-ago ancestor by a decent amount (a GD of 10 to 15, for example). But some will diverge much less, while others will diverge much more. It's really just luck.